Solid electrolytic capacitor

ABSTRACT

Disclosed is a solid electrolytic capacitor, comprising a capacitor element, an anode wire extended from a first side of the capacitor element in a predetermined length, and an anode lead frame formed as an anode terminal. The anode lead frame has a groove at a first end thereof for mounting an end portion of the terminal end of the anode wire thereon, and is mounted at a second end thereof on a PCB. A cathode lead frame is formed as a cathode terminal. This cathode lead frame has a first end attached to an external surface of the capacitor element and a second end mounted on the PCB. An epoxy case covers the capacitor element, the anode lead frame, and the cathode lead frame. The anode wire is welded to the anode lead frame by melting a portion of the anode lead frame in contact with an end portion of the anode wire positioned on the groove, using a heat source. This solid electrolytic capacitor is advantageous in that the heat transfer to the capacitor element during a welding step is minimized, the production process of the capacitor is simplified, and the capacitance of the capacitor element is enlarged by increasing the space occupied by the capacitor element within a limited space of the epoxy case.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates, in general, to a solidelectrolytic capacitor and, in particular, to an improved solidelectrolytic capacitor, which comprises a capacitor element with acapacitance increased by enlarging the space occupied by the capacitorelement within a limited space of an epoxy case, and anode lead framewhich can minimize the heat transfer to the capacitor element during anassembly of a capacitor element and a lead frame, simplifying theproduction process of the solid electrolytic capacitor.

[0003] 2. Description of the Prior Art

[0004] A solid electrolytic capacitor is an electronic device foraccumulating electricity, shielding a direct current, and passing analternating current. Among various solid electrolytic capacitors, atantalum capacitor is most widely applied to general industrialmachinery, and to an application circuit used in a low range of a ratedvoltage. In particular, the tantalum capacitor is used to reduce a noiseof a circuit or a portable communication apparatus in which a frequencycharacteristic is important.

[0005] The tantalum capacitor 100, as shown in FIGS. 1 to 4, comprises acapacitor element 110 consisting of dielectric powder which determinesthe capacitance and characteristic of a capacitor, an anode and acathode lead frame 130 and 140 connected to the capacitor element 110 soas to easily mount the capacitor on a printed circuit board (hereinafterreferred to simply as ‘PCB’), and an epoxy case 150 for protecting thecapacitor element 110.

[0006] A process of manufacturing the tantalum capacitor 100, comprisesthe steps of pressing tantalum powder into rectangularparallelepiped-shaped pellet, sintering and degassing the rectangularparallelepiped-shaped pellet, anodizing the pellet to form tantalumoxide (Ta₂O₅) layer on the exposed tantalum surfaces, infiltrating amanganese nitrate solution into the pellet, and thermally decomposingthe infiltrated pellet to form a manganese dioxide layer, that is, asolid electrolyte on a surface of the resulting pellet.

[0007] A process of connecting the anode and cathode lead frame 130 and140 to the capacitor element 110 thus manufactured comprises the stepsof welding a rod-shaped anode wire 120 protruded in a predeterminedlength from a lateral side of the capacitor element 110 to aplate-shaped anode lead frame 130 by an electrical spot welding processto form an anode terminal, and soldering the cathode lead frame 140 toan external surface of the capacitor element 110 with the use of aconductive adhesive such as carbon or silver powder coated on theexternal surface of the capacitor element 110 to form a cathodeterminal(See Japanese Laid-Open Patent Publication No. 5-335189 inventedby Honda Hisafumi et al.). Thereafter, the capacitor element 110electrically connected to the anode and cathode lead frame 130 and 140is molded with epoxy powder in an enveloping step so as to form an epoxycase 150 for protecting the capacitor element 110, and subjected to amarking step which ends the manufacturing process of the capacitor 100.

[0008] However, the conventional process of welding the anode wire 120to the anode lead frame 130 while they are in contact with an upper anda lower electrodes 161 and 162, indispensably comprises a bending stepof forming a flat pressed surface 122 on an external side of the anodewire 120 before welding of the anode wire to the anode lead frame inorder to prevent shaking occurring in welding, and to increase a contactefficiency between them. The conventional process is thusdisadvantageous in that an external mechanical impact readily occurringin the bending step is transferred through the anode wire 120 to thecapacitor element 110 destroying the dielectric layer. As a result, theelectrical property of the capacitor, for example, an LC value isdegraded. In addition, the production cost of the capacitor is increasedowing to the bending step.

[0009] In addition, in case that the anode wire 120 is welded to theanode lead frame 130 with the aid of the metal such as lead or tin, saidmetal can be melted due to the high temperature generated in the use ofthe set product where the capacitor is mounted. Thus, electrical openingcan occur undesirably in the set product.

[0010] Furthermore, a conventional process of soldering an externallower side of the capacitor element 110 to an upper side of the cathodelead frame 140 through the agency of a conductive adhesive isdisadvantageous in that the space occupied by the capacitor element 110within a limited space of an epoxy case 150 is relatively small, and a-volume of the capacitor element 110 is small, thereby the capacitanceof the capacitor 100 becomes small and the impedance is increased.

[0011] Meanwhile, the anode wire 120 of the capacitor element 110 may bewelded to the anode lead frame 130 by a laser welding process instead ofthe electrical spot welding process as disclosed in Japanese Laid-OpenPatent Publication No. 8-195330 invented by Mitsui Koichi et al. Morespecifically, a V-shaped notch part 132 is formed on the anode leadframe 130, the anode wire 120 of the capacitor element 110 is mounted onthe notch part 132, and portions of the frame 130 located at both sidesof the anode wire 120 are melted by a laser beam to weld the anode wire120 to the anode lead frame 130, as shown in FIGS. 5a to 5 c.

[0012] However, when the anode wire 120 is welded to the anode leadframe 130 by the laser beam, the welding process is very complicatedbecause the laser beam is simultaneously irradiated to two portions ofthe frame 130 located at both sides of the anode wire 120.

[0013] In addition, because the portions irradiated by the laser beamare restricted to a cut section of the notch part 132 corresponding tothe thickness of the anode lead frame 130, an area for welding the anodewire 120 to the anode lead frame 130 is small, and so the laser outputof the laser welding machine should be increased in order to increasewelding efficiency. At this time, a spark occurring during the laserwelding may reach the capacitor element 110, damaging the capacitorelement 110.

[0014] Moreover, the external surface of the anode lead frame 130 has ahigh absorbability of the laser beam because the external surfaceusually has a dark gray color, and so the welding characteristic thereofis excellent, but the notch part formed in a shape of ‘V’, having acolor of an inner metal of the anode lead frame 130 has a poorabsorbability of the laser beam and a high reflectivity against thelaser beam, and so the welding characteristic thereof becomes poor.Accordingly, the laser output of the laser welding machine is increasedin order to improve the welding efficiency, and thus consumption ofelectricity is increased, and heat impact and sparks transferred to thecapacitor element 110 are increased, thereby damage to the element isincreased.

SUMMARY OF THE INVENTION

[0015] Therefore, it is an object of the present invention to avoid theabove disadvantages, and to provide a solid electrolytic capacitor,which can avoid a bending process, minimize the heat transfer to itscapacitor element in order to obtain a stable electrical characteristic,increase its operational reliability, and reduce its production costowing to a simplified production process of the solid electrolyticcapacitor.

[0016] It is another object of the present invention to provide a solidelectrolytic capacitor, which can sufficiently enlarge the capacitanceof its capacitor element by increasing the space occupied by thecapacitor element within a limited space of an epoxy case.

[0017] It is still another object of the present invention to provide asolid electrolytic capacitor, which can improve welding efficiencybetween a lead frame and an anode wire by preventing a shaking of theanode wire.

[0018] Based on the present invention, the above objects can beaccomplished by a provision of a solid electrolytic capacitor,comprising a capacitor element; an anode wire extended from a first sideof the capacitor element in a predetermined length; an anode lead framewhich has a groove at a first end thereof for mounting an end portion ofthe anode wire thereon and a second end thereof for mounting on a PCB; acathode lead frame which has a first end attached to an external surfaceof the capacitor element and a second end for mounting on the PCB; and amold case, preferably an epoxy case covering the capacitor element, theanode lead frame, and the cathode lead frame. In the capacitor, theanode wire is welded to the anode lead frame by melting a portion of theanode lead frame in contact with the end portion of the anode wirepositioned on the groove, using a heat source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

[0020]FIG. 1 is a perspective view of a conventional solid electrolyticcapacitor;

[0021]FIG. 2 is a sectional view of the conventional solid electrolyticcapacitor;

[0022]FIG. 3 is a plan view of the conventional solid electrolyticcapacitor;

[0023]FIG. 4 is a view illustrating a conventional solid electrolyticcapacitor;

[0024]FIGS. 5a to 5 c are a plan view, an elevational view, and a sideview of the conventional solid electrolytic capacitor engaged with alead frame having a notch part, respectively;

[0025]FIG. 6 is a perspective view of a solid electrolytic capacitoraccording to the first embodiment of the present invention;

[0026]FIG. 7 is a sectional view of the solid electrolytic capacitoraccording to the first embodiment of the present invention;

[0027]FIG. 8 is a plan view of the solid electrolytic capacitoraccording to the first embodiment of the present invention;

[0028]FIG. 9 is a view illustrating a solid electrolytic capacitoraccording to the first embodiment of the present invention;

[0029]FIGS. 10a and 10 b are a plan view and an elevational view of anarc-shaped groove adopted in the solid electrolytic capacitor accordingto the first embodiment of the present invention, respectively;

[0030]FIGS. 11a and 11 b are a plan view and an elevational view of arectangular groove adopted in the solid electrolytic capacitor accordingto a modification of the first embodiment of the present invention,respectively;

[0031]FIGS. 12a and 12 b are a plan view and an elevational view of atriangular groove adopted in the solid electrolytic capacitor accordingto another modification of the first embodiment of the presentinvention, respectively;

[0032]FIG. 13 is a perspective view of a solid electrolytic capacitoraccording to the second embodiment of the present invention;

[0033]FIG. 14 is a sectional view of the solid electrolytic capacitoraccording to the second embodiment of the present invention;

[0034]FIG. 15 is a plan view of the solid electrolytic capacitoraccording to the second embodiment of the present invention; and

[0035]FIG. 16 is a side view of the solid electrolytic capacitoraccording to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0036]FIG. 6 is a perspective view of a solid electrolytic capacitoraccording to the first embodiment of the present invention, FIG. 7 is asectional view of the solid electrolytic capacitor according to thefirst embodiment of the present invention, FIG. 8 is a plan view of thesolid electrolytic capacitor according to the first embodiment of thepresent invention, and FIG. 9 is a view illustrating a solidelectrolytic capacitor manufactured according to the first embodiment ofthe present invention.

[0037] With reference to FIGS. 6 to 9, the solid electrolytic capacitor1 of the present invention has an improved structure in which acapacitor element 10 is electrically welded to an anode and a cathodelead frame 30 and 40, which results in stable electrical characteristicsof the capacitor element 10, and an enlarged capacitance of thecapacitor element 10 is obtained by increasing the relative volume ofthe capacitor element 10 within a limited space of the capacitor.

[0038] The capacitor element 10 is a dielectric element produced bycompressing tantalum powder in a shape of a rectangular parallelepiped,and the anode and the cathode lead frame 30 and 40 are terminal memberseach consisting of a metal material with an excellent electricalconductivity. An anode wire 20 is extended from a first side of thecapacitor element 10 in a predetermined length.

[0039] Various materials such as niobium(Nb) oxide are selectively usedas the capacitor element adopted in the solid electrolytic capacitor,and the material of the capacitor element is not restricted totantalum(Ta) oxide.

[0040] A groove 32 is formed on a first end of the anode frame 30 forpartially mounting the end portion of the anode wire 20, and a secondend of the anode frame 30 is formed as an anode terminal for mountingthe capacitor on a PCB. At this time, the groove 32 is formed bypressing so as to be downwardly depressed during the production processof the anode lead frame.

[0041] The cathode lead frame 40 opposite to the anode lead frame 30 isattached to an external surface of the capacitor element 10 through theagency of a conductive adhesive at a first end thereof, and is mountedon the PCB at a second end thereof to be formed as a cathode terminal.The capacitor element 10, the anode and the cathode lead frame 30 and 40are housed in an epoxy case 50, thereby being protected from theenvironment.

[0042] The anode wire 20 is mounted on the groove 32 in such a way thatit is in close a contact with the vertical side of the anode lead frame32 positioned around the groove 32, and a laser beam from a laserwelding machine is irradiated as a high temperature heat source to aportion of the anode lead frame 30 positioned around the end portion ofthe anode wire 20.

[0043] Because the anode lead frame 30 consists of a metal material suchas iron having a lower melting point than tantalum constituting theanode wire 20, a portion of the vertical side of the anode lead frame 30is melted by the heat source irradiated to the portion of the anode leadframe 30 positioned around the end portion of the anode wire 20.However, the anode wire 20 in such a case is not melted, and the anodewire 20 is welded to the anode lead frame 30.

[0044] In other words, the end portion of the anode wire 20 is directlywelded to the anode lead frame 30 by a frame melt without the aid of themetal such as lead, thereby preventing problems such as damage or anelectrical opening owing to the melting of the metal caused by a hightemperature during the use of a product adopting the capacitor of thepresent invention.

[0045] Additionally, a heat transfer path, along which heat generated inlaser welding step is transferred to the capacitor element 10 throughthe terminal side of the anode wire 20, can be considerably lengthened.In addition, the external surface of the anode wire 20 is mostly coveredwith the groove 32, and so the heat generated around the welded area isabsorbed by the frame surrounding the wire, thus minimizing the heattransferred to the capacitor element 10. Therefore, the heat impact tothe capacitor element 10 is minimized. Furthermore, the capacitorelement 10 of the present invention becomes larger than that of aconventional structure in which the terminal end of the anode wire 20 iselectrically welded to the anode lead frame 30 by reducing the length ofthe anode wire 20 in the epoxy case 50, which results in an enlargedcapacitance of the capacitor element 10.

[0046] The laser welding machine may be positioned on a vertical line‘P’ at right angles to the center ‘O’ of the anode wire 20, and providesa heat source melting the vertical side of the anode lead frame 30opposite to the terminal end of the anode wire 20. At this time, thecenter ‘O’ of the anode wire 20 mounted on the groove 32 coincides withthe center of a laser beam, that is, the heat source irradiated from thelaser welding machine, and thus the concentration degree of the laserbeam melting the anode lead frame 30 is increased, thereby the weldingprocess is accurately accomplished.

[0047] Alternatively, the laser welding machine may be positioned underthe anode wire 20 and provides the heat source in a direction ‘W’indicated by the arrow to an external lower side of the groove 32 onwhich the end portion of the anode wire 20 is mounted, as shown in FIG.9. At this time, a spark generated upon welding of the anode lead frame20 using the laser beam is prevented from reaching the tantalum element10 by the blocking of the anode lead frame 30, thereby damage to thetantalum element 10 is prevented.

[0048] Meanwhile, the anode lead frame 30 is depressed by apredetermined external force to form the groove 32 on which the endportion of the anode wire 20 is partially mounted, in order to prevent ajoggle of the anode wire 20 during the welding and accomplish anaccurate welding process. It is preferable that the groove 32 ispositioned at the center of a width of the first end of the anode leadframe 30 which is located on the same vertical line as the center of theheat source such as the laser beam of the laser welding machine.

[0049] The groove 32 may be formed with a circular arc shapedcross-section so as to be in contact with a circumferential surface ofthe rod-shaped anode wire 20, as shown in FIGS. 10a and 10 b.Alternatively, the groove 32 may be formed with a polygonalcross-section such as a triangle and a quadrangle so as to be in contactwith the circumferential surface of the rod-shaped anode wire 20 at twoor more contact points, as shown in FIGS. 11a to 12 b.

[0050] The anode wire 20 mounted on the groove 32 is preferably formedwith the same cross-sectional shape as the groove 32 so as to improvethe heat removing ability of the anode lead frame 30 by increasing thecontact area between the external surface of the anode wire and theinternal surface of the groove 32.

[0051] The depth ‘h’ of the groove 32 is less than the outer diameter‘d’ of the anode wire 20, so that the upper portion of the anode wire 20is partially protruded outside of the groove 32, and also the outerdiameter ‘d’ of the anode wire 20 is preferably smaller than the width‘b’ of the groove 32. At this time, a frame melt does not flow to theoutside of the groove 32, but smoothly flows between the anode wire 20and the anode lead frame 30 to improve the weldability between the anodewire 20 and the anode lead frame 30.

[0052]FIG. 13 is a perspective view of the solid electrolytic capacitoraccording to the second embodiment of the present invention, FIG. 14 isa sectional view of the solid electrolytic capacitor according to thesecond embodiment of the present invention, FIG. 15 is a plan view ofthe solid electrolytic capacitor according to the second embodiment ofthe present invention, and FIG. 16 is a side view of the solidelectrolytic capacitor according to the second embodiment of the presentinvention.

[0053] According to the second embodiment of the present invention, thesolid electrolytic capacitor 1 a is characterized in that a cathode leadframe 40 led as a cathode terminal has a flat contact plate 42positioned on the first end thereof, in contact with the vertical sideof the capacitor element 10 through an agency of a conductive adhesive,as shown in FIGS. 13 to 16.

[0054] The contact plate 42 with a ‘T’-shaped cross-section is formed bybending an inside portion, which is formed by cutting along a ‘U’-shapedcutting line 44 drawn on a surface of the first end of the cathode leadframe 40, in an upward and vertical direction, and by bending aremaining part of the first end of the cathode lead frame 40 around endsof the cutting line 44 in a downward and vertical direction.

[0055] In this case, the contact plate 42 is in contact with the mostarea of the vertical side of the capacitor element 10 to form a broadcontact area, thereby a short circuit is prevented. Furthermore, bymoving the contact location of the cathode lead frame to the verticalside, the height of the capacitor element 10 of the present inventionbecomes longer than that of a conventional structure in which the firstend of the cathode lead frame 140 is soldered to a flat lower part ofthe capacitor element 110. This increased volume of the capacitorelement 10 results in an enlarged capacitance of the capacitor element10.

[0056] It is preferable that the welding step of the anode wire 20 tothe anode lead frame 30 is accomplished after the soldering step of thecapacitor element 10 to the cathode lead frame 40. At this time, a framemelt having flowed between the anode wire 20 and the anode lead frame 30prevents the capacitor element 10 from longitudinally deforming, therebyan assembly of the capacitor element and the lead frame is accuratelyaccomplished.

[0057] Therefore, the present invention is advantageous in that an anodewire is mounted on a groove of an anode lead frame without shaking ofthe anode wire, and welded to the anode lead frame by a heat source suchas a laser beam, thereby a bending process necessarily accompanied in aconventional electric spot welding process can be omitted and so theproduction cost of the solid electrolytic capacitor of this inventioncan be reduced.

[0058] Other advantages of the present invention are that the heattransfer to a capacitor element is minimized by removing heat generatedby a welding process, and the electric characteristics of the capacitorelement are stabilized by preventing mechanical impact and thus theoperational reliability of this solid electrolytic capacitor can beimproved. Furthermore, the capacitor element becomes relatively large insize by increasing the space occupied by the capacitor element in anepoxy case for protecting the capacitor element, which results in anenlarged capacitance of the capacitor element.

[0059] The present invention has been described in an illustrativemanner, and it is to be understood that the terminology used is intendedto be in the nature of description rather than of limitation. Manymodifications and variations of the present invention are possible inlight of the above teachings. Therefore, it is to be understood thatwithin the scope of the appended claims, the invention may be practicedotherwise than as specifically described.

What is claimed is:
 1. A solid electrolytic capacitor, comprising: acapacitor element; an anode wire extended from a first side of thecapacitor element in a predetermined length; an anode lead frame havinga groove at a first end thereof for mounting an end portion of the anodewire, and a second end thereof for mounting on PCB as an anode terminal;a cathode lead frame having a first end attached to an external surfaceof the capacitor element and a second end for mounting on a PCB; and amold case covering the capacitor element, the anode lead frame, and thecathode lead frame, wherein said anode wire is welded to the anode leadframe by melting a portion of the anode lead frame in contact with theend portion of the anode wire positioned on said groove, using a heatsource.
 2. The solid electrolytic capacitor according to claim 1,wherein the heat source is a laser beam melting the anode lead frame,irradiated from a laser welding machine positioned above said groove. 3.The solid electrolytic capacitor according to claim 1, wherein the heatsource is a laser beam melting the anode lead frame, irradiated from alaser welding machine positioned under the anode lead frame.
 4. Thesolid electrolytic capacitor according to claim 1, wherein the anodelead frame consists of a metal material with a lower melting point thanthat of the anode wire.
 5. The solid electrolytic capacitor according toclaim 1, wherein the cathode lead frame has a contact plate at the firstend thereof, said contact plate being in contact with a vertical secondside of the capacitor element through an agency of a conductiveadhesive.
 6. The solid electrolytic capacitor according to claim 5,wherein the contact plate with a ‘T’-shaped cross-section is formed bybending an inside portion, which is formed by cutting along a ‘U’-shapedcutting line drawn on a surface of the first end of the cathode leadframe, in an upward and vertical direction, and by bending a remainingpart of the first end of the cathode lead frame around ends of thecutting line in a downward and vertical direction
 7. The solidelectrolytic capacitor according to claim 1 or 5, wherein said groovehas a circular arc-shaped cross-section so as to be in contact with acircumferential surface of the anode wire.
 8. The solid electrolyticcapacitor according to claim 1 or 5, wherein said groove has a polygonalcross-section so as to be in contact with a circumferential surface ofthe anode wire at two or more points.
 9. The solid electrolyticcapacitor according to claim 1 or 5, wherein a depth of the groove isless than an outer diameter of the anode wire mounted thereon so that anupper portion of the anode wire is partially protruded outside of thegroove.
 10. The solid electrolytic capacitor according to claim 1 or 5,wherein said anode wire mounted on the groove has the samecross-sectional shape as the groove.
 11. A solid electrolytic capacitor,comprising: a capacitor element; an anode wire extended from a firstside of the capacitor element in a predetermined length; an anode leadframe having a first end thereof connected to an end portion of theanode wire, and a second end thereof for mounting on PCB as an anodeterminal; a cathode lead frame having a contact plate at the first endthereof and a second end for mounting on a PCB, wherein said contactplate is in contact with a vertical second side of the capacitorelement, and has a ‘T’-shaped cross-section formed by bending an insideportion, which is formed by cutting along a ‘U’-shaped cutting linedrawn on a surface of the first end of the cathode lead frame, in anupward and vertical direction, and by bending a remaining part of thefirst end of the cathode lead frame around ends of the cutting line in adownward and vertical direction; and a mold case covering the capacitorelement, the anode lead frame, and the cathode lead frame.